The present invention relates generally to a detector system, and, more particularly to a two dimensional (2D) collimator assembly which may be employed in a detector system.
Computed tomography (CT) is utilized for a wide variety of imaging applications, such as medical imaging. CT systems are imaging systems that are generally configured to transmit x-rays through a structure, such as a human body, to detect and diagnose abnormalities, such as tumors. These low energy x-rays are subsequently received and processed to formulate an image, often three-dimensional, of the body structure that can by analyzed by clinicians as a diagnostic aid.
The reception of the radiation, such as gamma rays or x-rays, is often accomplished through the use of a device such as a detector assembly. The detector assembly is typically comprised of a plurality of structures working together to receive and process the incoming energy rays after they have passed through the body structure. The detector assembly utilizes a scintillator assembly to convert incident radiation, such as x-rays, into light for detection at an array of light detection devices. Scintillation allows the radiation received by the scintillator assembly to be converted into useful information. Scintillator assemblies may come in a wide variety of forms and may be adapted to receive a wide variety of incoming rays. The light produced by the scintillator assembly is commonly received (or “detected”) and processed by a detection device such as a light sensitive photodiode, which converts the light from the scintillator assembly into an electronic signal. The information from the scintillator assembly can be easily transferred, converted, and processed by electronic modules in a data acquisition system to facilitate viewing and manipulation by clinicians.
Typically, detector assemblies also include a collimator assembly. A collimator assembly is typically designed to reduce x-ray scatter and/or shield the underlying elements from undesirable exposure. The collimator assembly is used to reduce x-ray scatter as the x-rays approach the scintillator element. Scattered photons can cause excess noise and artifacts in the reconstructed CT images. In addition, the collimator is commonly used as a shielding device for shielding the edges of the individual scintillator cells and to prevent x-rays from impinging on the edges of the scintillators causing non linearities and image artifacts. The collimator may also be employed to prevent x-rays from damaging the reflector between scintillator elements, to prevent x-rays from being transmitted through the gap between scintillator elements and impinging on the photo diode causing noise and/or to prevent x-rays from being transmitted through the gap between scintillator elements and impinging on electronics located behind the detector causing damage to these sensitive electronic components. Thus, present collimator assembly designs commonly attempt to balance shielding and scatter reducing properties.
Currently, CT collimator assemblies are 1-dimensional (1D) arrays assembled from long, thin metal blades, such as tungsten blades. In conventional systems these blades are >75 mm long, 200 um thick, and 7-8 mm tall. Approximately 1000 of these blades are assembled onto a precisely machined support rail to create a complete collimator assembly. While useful for scatter reduction and shielding, typical 1D collimator assemblies have a number of disadvantages. The assembly process is often tedious, and the cost of assembly is a significant fraction of the total cost of the collimator. In addition, at high gantry rotation rates, the tungsten blades deflect and cast shadows onto part of each detector pixel, causing gain-error artifacts in the image. Further, current collimator assembly designs are not easily extended to wider detectors (more slices) because of the mechanical stability of the blades. As desired detection areas grow, this shortcoming becomes an increasingly significant obstacle. Still further, the total amount of scatter impinging on the collimator increases roughly in proportion to the z-coverage of the detector. At the coverage that will soon be desired, the ability of the 1D collimator to reject the incoming scatter becomes increasingly inadequate.
Therefore, there is currently a need for a collimator assembly that provides for wider scanning areas, improved structural durability and simpler fabrication techniques.